A conventional method for arranging hole patterns is described below:
FIG. 8 shows pattern drawings showing examples of hole pattern arrangement formed on a photomask.
As shown in FIG. 8A, since a focus margin is not broad enough in the layout where hole patterns 10 are arranged arbitrarily, an arrangement of auxiliary patterns, which are not transferred onto a photoresist layer during an exposure process, is necessary. (Refer to Patent Document 1 for example.)
As shown in FIG. 8B, in the case where auxiliary patterns 12 are arranged as densely as possible, problems where the auxiliary patterns are transferred onto a photoresist layer during an exposure process and the auxiliary patterns are connected with each other at the positions indicated by solid lines can occur. Also, problems where the shapes of the hole patterns 10 transferred onto a photoresist layer are distorted and the hole patterns 10 and the auxiliary patterns 12 are connected at the positions indicated by broken lines can occur.
On the other hand, if the minimum necessary numbers of the auxiliary patterns 12 are provided as shown in FIG. 8C, the problems described above can be avoided, but the effect of broadening the focus margin cannot be fully obtained.
The size of the auxiliary patterns 12 should be approximately 80% of the size of the hole patterns from the standpoints of the manufacturing accuracy of a reticle, which is going to be a photomask, the defect inspection accuracy, and the effect of broadening a transfer margin and the focus margin. Also, the distance between the gravity centers of the hole patterns 10 and the auxiliary patterns 12 must be approximately the same as the densest pitch, which is the minimum value of the distance between the gravity centers of the hole patterns 10 from the standpoint of the effect of broadening the focus margin.
Further, it is known that the effect of broadening the focus margin cannot be fully obtained unless the arrangement of the auxiliary patterns 12 is isotropic in all directions as much as possible. In order to achieve this, techniques such as adjusting the size of the auxiliary patterns 12 and adjusting the distance between the auxiliary patterns 12 and the hole patterns 10 are employed. In FIG. 8D, the size of the auxiliary patterns 12 is decreased. FIGS. 8B through 8D show the auxiliary patterns 12 provided around the center of the pattern drawing.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-A-11-135402